1. Field of the Invention
This invention relates to the recovery of lead from lead sulfide-containing materials and more particularly to a relatively low temperature, non-SO.sub.2 polluting process which is carried out in a kettle or the like, for instance a kettle ordinarily on hand in a lead refinery, and which does not require a smelting furnace or the relative high temperatures of smelting.
2. Description of the Prior Art
U.S. Pat. No. 816,773 discloses a smelting process for recovering lead from lead sulfide ore. The lead sulfide ore is smelted in a smelting furnace with a material containing a heavy metal such as iron, a carbon reducing agent, and an alkali metal, thereby producing metallic lead, an iron-alkali metal matte, and a slag containing less than five percent of ferrous oxide. U.S. Pat. No. 599,310 relates to a process for extracting lead with other metals from its ores involving mixing and heating the ore in a furnace such as a Siemens open hearth gas furnace with an alkali metal sulfate, carbonaceous material, preferably particulate coal, and oxide of zinc to fuse the mixture. The lead, which contains most of the silver and gold, is tapped off, and the zinc is volatilized and collected as zinc oxide in the furnace flue. U.S. Pat. No. 821,330 discloses a process of smelting lead sulfide ores comprising preparing a smelting charge consisting of lead sulfide ore, iron oxides, sodium sulfide or a material yielding sodium sulfide, and carbon or carbon compounds, e.g. coal or coke, and smelting the charge in preferably a reverberatory smelting furnace. U.S. Pat. No. 2,110,445 discloses a process for purifying lead bullion containing the usual small amounts of arsenic, copper, tin, antimony, bismuth and noble metals involving adding a small amount of metallic sodium to a molten bath of the bullion. The dross is thereafter skimmed from the bath at a temperature of about 330.degree. C. thereby obtaining a lead containing a less than 0.01% arsenic and less than 0.005% copper. U.S. Pat. No. 2,691,575 discloses a process for converting lead oxide to lead and particularly to the treatment of lead oxide slags obtained in the refining of impure by-product lead produced in the manufacture of tetraethyl lead. The process comprises heating a fluid mixture of lead oxide and sodium hydroxide at temperatures of from 327.degree. C. to about 450.degree. C., mixing with such mixture about 10% to about 30% by weight of metallic sodium based on the lead oxide, and separating molten lead from the reaction mixture. U.S. Pat. No. 4,033,761 discloses a process for the separation of copper sulfide from metallic lead mechanically entrained in a rough copper dross obtained from the copper drossing of lead bullion, involving heating the dross and an alkali metal sulfide together in a kettle at an elevated temperature not in excess of 1200.degree. F. to melt together the dross and alkali metal sulfide. The thus-obtained molten dross releases the entrained molten lead which passes to the kettle bottom, and the copper sulfide of the molten dross and the alkali metal sulfide form a low melting copper sulfide-alkali metal sulfide matte layer on the surface of a pool of the released molten lead. Although this process yields good results in separating copper sulfide and entrained metallic lead from rough copper dross, it is unsatisfactory when the rough copper dross also contains a significant quantity of lead sulfide and the aim or purpose is to recover the lead of the lead sulfide by reducing such sulfide to metallic lead in addition to separating the copper sulfide and releasing the entrained metallic lead. The reason the process of U.S. Pat. No. 4,033,761 is unsatisfactory for recovering the lead from lead sulfide in such dross is that the process will not reduce the chemically combined lead of the lead sulfide to zero valent, elemental lead.
The prior art smelting processes generated polluting SO.sub.2 which was discharged into the atmosphere.